This invention relates to poly(arylene ether) polymers bearing grafted hydroxyalkyl group(s), compositions containing them, and to the use of such polymers and compositions in adhesives, sealants, coatings, and particularly electrically conductive adhesives.
Electronic packaging is an essential part of making technologies available to the everyday consumer. Although a lot of rapid advancements have been made to make integrated circuits (IC) chips smaller and faster, improvements must also be made to package the chips.
There are four main functions to electronic packaging. See, e.g., J. H. Lau, “A Brief Introduction Flip Chip Technologies for Multichip Module Applications,” Flip Chip Technologies, J. H. Lau (Ed.), McGraw-Hill, N.Y., 1995. The first is to provide a path for electrical currents that provide power to the circuits on the chip. The second function is to distribute signals to and from the IC chip. The third is to remove heat generated by the circuit. The last function is to support and protect the chip from unfavorable conditions, such as extreme temperatures and wear.
There are four different levels of electronic packaging. See, e.g., R. Tummala, “Microelectronics Packaging—an Overview,” Microelectronics Handbook, Part 1, (R. Tummala et al., Eds.), Ed. International Thompson Publishing, 2nd Edition, New York, 1997. The zero level is connections on the chip level, or wafer level. The first level is the connection from the chip to a single or multi chip module. The second level is the connection from the first level module to printed circuit boards. Finally, the third level is the connection to a motherboard.
In the first and second levels of electronic packaging, tin/lead solder is one of the important materials for making interconnection. Its process parameters are well established in the industry and its cost is relatively inexpensive. Electronic packages that use tin/lead eutectic solder have very reliable thermal, electrical, and mechanical performance.
Despite the advantages of tin/lead solder, there are two factors that have prompted the research for alternative interconnect materials. The first factor is the increasing demands to increase the I/O density in electronic packages, which result in smaller feature sizes and smaller products. The second factor is the desire to ban or reduce lead usage in industrial manufacturing processes and products.
There are two main lead-free alternatives to tin/lead eutectic solder for interconnect material. The first is lead-free solder and the second is electrically conductive adhesive (ECA). Lead-free solder is considered a short term replacement for eutectic solder, since the technology capability of that category of material also is limited by the solder stencil printing process. ECA is a composite of polymer filled with conductive particles, and it is considered a long-term replacement for tin-lead solder.
There are two types of ECAs: isotropic conductive adhesive (ICA) and anisotropic conductive adhesive/film (ACA/ACF). See, e.g., K. Gilleo, “Introduction to Conductive Adhesive Joining Technology,” Conductive Adhesives for Electronics Packaging, J. Liu (Ed.), Electrochemical Publications, British Isles, 1999. ICA has conductivity in all directions, and is also often called “polymer solder.” ACA/ACF systems only have conductivity in one direction. Generally, ICAs have higher conductivity than ACA/ACF, so ICAs have generally been considered to be the more promising replacements for tin/lead solder in high performance applications. R. Ghaffarian, “Close the Information Gap on IC-Package Reliability,” Electronic Design, vol. 46, no.18, pp. 71–72, Aug. 3, 1998.
The adhesive generally selected for ICA is thermosetting epoxy resin because of its excellent adhesion properties, and because it is relatively stable up to 200° C. Id. Thermoplastics are used in ICAs, but they are mostly applied in die attach, where the important functionality is thermal conductivity. See, e.g., J. Ivan et al., “Moisture and Thermal Degradation of Cyanate-Ester-Based Die Attach Material,” Proceedings of the 1997 Electronic Components and Technology Conference, 1997, pp. 525–535; I. Y. Chien et al., “Low Stress Polymer Die Attach Adhesives for Plastic Packages,” Proceedings of the 1994 Electronic Components and Technology Conference, 1994, pp. 580–584; D. P. Galloway et al., “Reliability of Novel Die Attach Adhesives for Snap Curing,” Proceedings of the IEEE/CPMT International Electronic Manufacturing Technology (IEMT) Symposium, 1995, pp. 141–147; and A. Javidinejad et al., “Application of Electrically Conductive Thermoplastic Adhesive Film for Design and Manufacturing of Smart Structures,” SPIE Proceedings Smart Structures and Integrated Systems, Vol. 3668, March 1999, pp. 688–695. As for the conductive fillers, silver flakes are used because its resistivity is very low and its oxide is conductive. See, e.g., D. Lu et al., “Conductive Adhesives Based on Anhydride-Cured Epoxy Systems,” Proceedings of the 2nd International IEEE Symposium on Polymeric Electronics Packaging, 1999. The concentration of conductive fillers in ICA formulation is just beyond the percolation critical volume fraction, between 25 to 30 vol. %. See, e.g., K. Gilleo, “Assembly with Conductive Adhesives,” Soldering and Surface Mount Technology, No. 19, February 1995, pp. 12–17; and P. G. Hariss, “Conductive Adhesives: A Critical Review of Progress to Date,” Soldering and Surface Mount Technology, No. 20, May 1995, pp. 19–21.
Although ICAs are not as well established as tin/lead solder as interconnect material, this technology has a lot of advantages over solder (lead and lead-free). The major advantages include the absence of lead, fine pitch capability, reduction in the number of processing steps, low process temperature, and no soldermask requirements. J. C. Jagt et al., “Electrically Conductive Adhesives: A Prospective Alternative for SMD Soldering?” IEEE Transactions on Components, Packaging, and Manufacturing Technology—Part B Advanced Packaging, Vol. 18, no. 2, pp. 292–297, May 1995.
The main drawbacks of ICAs are low conductivity, unstable contact resistance, poor impact performance, and lack of reworkability. See, e.g., J. Jagt, “Reliability of Electrically Conductive Adhesive Joints for Surface Mount Applications,” IEEE Transactions on Components, Packaging, and Manufacturing Technology—Part A, Vol. 21, No. 2, pp. 215–225, June 1998.
Accordingly, it is desired to provide ICAs with acceptable conductivity, stable contact resistance, good impact performance and/or acceptable reworkability.
All references cited herein are incorporated herein by reference in their entireties.